During oilfield drilling and borehole completion operations tubular strings may be handled in the form of the drill string, the casing or liner string for lining the borehole, etc. To grip the tubular and the tubular string, a tubular gripping clamp tool may be used. In some operations, such as casing drilling and/or casing running, a casing clamp may be used to grip the string at its upper end.
Sometimes an inside gripping clamp may be used. An example of such a gripping clamp is described in U.S. Pat. No. 6,742,584 of Appleton, and assigned to the present assignee TESCO Corporation. Alternately, an external gripping clamp may be used. As an example, such a gripping clamp is described in U.S. Pat. No. 6,311,792 of Scott, which is also assigned to the present assignee.
A tubular gripping clamp may be connected for manipulation by a top drive or other device, the entire assembly being suspended in a rig or derrick by a draw works, if desired.
Tubular gripping tools may include gripping means that engage the tubular being handled. Gripping means may include, for example, devices that mechanically or frictionally engage the tubular including, for example, slips, jaws, packers, expandable members, etc., catch devices that hook under a shoulder on the tubular being handled, such as elevators, etc. and/or other members that exert a mechanical or physical force or field on the tubular to engage it. Tubular gripping tools may also include spears, which are intended to extend into the bore of a tubular being handled. An external gripping tool may include a spear surrounded by gripping means that engage an outer surface of the tubular, while the spear is inserted into the inner diameter of the tubular. An inside gripping clamp may include a spear with gripping means thereon, such that when the spear extends into the bore of a tubular being handled the gripping means are positioned for engagement of the inner wall of the tubular.
A spear of a tubular gripping clamp may include a seal thereabout which is selected to engage and create a seal against the inner diameter of the tubular being handled. During operation, drilling fluid, commonly called mud and which can be liquid or gas-based, is pumped down through the spear and the seal creates a seal against the inner diameter to maintain fluid pressure in the tubular string. The seal generally is passive and operates against a pressure differential.
In a well control incident, it may be desirable to shut in the well, including sealing the upper end of the tubular string. If such an incident occurs during the use of a gripping clamp, well control may be achieved by reliance on the seal about the clamp's spear. As a next step, or where a failure of the passive seal is encountered, it may be desirable to support the tubular string in the floor of the derrick/rig and to remove the casing clamp from the tubular, such that the tubular string can be capped.
In the situation where both the draw works and the spear seal fail, the well may be very difficult to control.